The present disclosure relates generally to induction heating, and more particularly to induction sealing in which a workpiece is sealed, for example, to another structure, via inductive heating of a heat-sealable material disposed therebetween. Still more particularly, the disclosure relates to induction sealing of lids, closures, caps, or the like, to containers such as cans, jars, bottles, or the like.
It is known to induction seal a lid or cap to a container. For example, U.S. Pat. No. 3,909,326 to Renck describes a method for applying a heat-sealable membrane to a mouth of a container. A heat-sealable packaging material, which preferably includes at least a heat-sealable membrane and a metal foil, is applied to the mouth of each container. A conveyor for conveying the containers is driven by means of a motor. A continuous belt spaced above the conveyor is driven by means of a drive assembly also coupled to the motor.
An overcap is also placed over the container so as to restrain the heat-sealable member and prevent its movement during movement of the container through the apparatus. The container with the heat sealable packaging material in place is then moved onto the conveyor. The conveyor passes the container into position under the continuous belt. The continuous belt is controlled to move at the same speed as the conveyor so that there is no differential motion between the continuous belt and the conveyor. The continuous belt presses down upon the mouth of the container and holds the heat-sealable packaging material tightly in position as the container is passed under an induction coil. The induction coil is energized with sufficient power to heat the metal foil laminate of heat-sealable member and to cause the metal foil laminate to attain a sufficient temperature to activate the heat-sealing membrane of the heat-sealable packaging material.
Variations in the type of apparatus and process described in the '326 patent have been proposed, mainly addressing ways of achieving intimate contact between the heat-sealable lid and the container mouth during induction heating and subsequent cooling; see, for example: U.S. Pat. Nos. 4,095,390; 5,562,799; and 5,858,141. While these developments in some cases have provided useful contributions to the state of the art, further improvement in induction sealing apparatuses and methods is sought.